The present invention relates to a vacuum processing apparatus that is used to subject a substrate to be processed, such as a semiconductor wafer, to a vacuum process.
Various steps in the formation of an integrated circuit on a semiconductor wafer are performed in a vacuum, such as film formation and etching. In such vacuum processing, the wafer is mounted onto a mounting stand within a vacuum chamber but, in order to maintain the wafer at a predetermined uniform temperature by a temperature adjustment means provided within the mounting stand, it is necessary to press the wafer against the mounting stand. Since it is not possible to use a vacuum chuck in a vacuum, another type of chuck such as an electrostatic chuck is used for attracting the wafer to the surface of the mounting stand by an electrostatic force, and holding it there.
A conceptual view of the entire structure of a vacuum processing apparatus, including a mounting stand, is shown in FIG. 7, taking a plasma processing apparatus that uses electron cyclotron resonance (ECR) by way of example. This vacuum processing apparatus supplies microwaves at, for example, 2.45 GHz into a plasma generation chamber 1A through a waveguide 11 and produces a magnetic field at, for example, 875 Gauss therein by an electromagnetic coil 12, so that the mutual actions of the microwaves and the magnetic field turn a plasma generation gas, such as argon or oxygen, into a high-density plasma. A reaction gas such as SiH4, which is introduced into a film-formation chamber 1B, is activated by this plasma to form a thin film on the surface of a semiconductor wafer W.
A mounting stand 10 used in this apparatus is configured so that a dielectric plate 15 is provided on an upper surface of a main mounting stand unit 13, which is made of a material such as aluminum, with an O-ring 14 made of a material such as fluoro-rubber therebetween. This dielectric plate 15 is provided internally with metal electrodes 16 of, for example, tungsten in the vicinity of the surface thereof, so that the surface portion is configured as an electrostatic chuck. Coolant passages (not shown in the figure) are also provided within the main mounting stand unit 13, and a heater 17 consisting of, for example, tungsten electrodes is provided within the dielectric plate 15. Since this mounting stand 10 will be disposed within a vacuum, the region enclosed by the O-ring 14 between the main mounting stand unit 13 and the dielectric plate 15 is arranged in such a manner that helium is supplied thereto to maintain a uniform thermal conductivity.
The thus configured mounting stand 10 is designed to attract and hold the wafer W to the mounting surface, as described above, but it also fulfills the role of heating the wafer W to a predetermined temperature and achieves a reference temperature by means of a coolant, so that the wafer is always controlled to have a constant temperature by the combination of that coolant and the heater 17.
However, since semiconductor devices are now being designed to operate at even faster speeds, the formation of an SiOF film, which has a lower permittivity than an SiO2 film, is being promoted for the inter-layer insulation films thereof. This SiOF film can be formed by the above described ECR plasma apparatus, but the processing is at a higher temperature than that for an SiO2 film and thus the temperature of the surface of the dielectric plate 15 reaches 320 to 330.degree. C. during the processing.
Since the dielectric plate 15 is a sintered body, it is difficult to construct to a greater thickness, so the thickness thereof is limited to at most about a dozen mm. In such a case, if the surface of the dielectric plate 15 is heated by the heater 17 to approximately 320.degree. C., the temperature of the rear surface side of the dielectric plate 15 on which the O-ring 14 is provided reaches approximately 300.degree. C. but, since the O-ring 14 is a resin product with a thermal resistance of no more than 200.degree. C., the O-ring 14 will deteriorate during this processing and the sealing ability thereof will no longer be maintained.
In addition, the insulation resistance of a dielectric body decreases as temperature increases, so that the insulation resistance of the dielectric plate 15 will decrease if the processing temperature is increased, electric charge remaining in the insulating film due to the electrostatic attraction, for example, will escape to ground through the wafer W during the processing, and thus there is a danger that the insulation of the inter-layer insulation film may break down.
The present invention was devised in the light of the above problems and has as an object thereof the provision of a vacuum processing apparatus that can suppress deterioration of the O-ring provided in the mounting stand and prevent breakdown of the insulating properties of an insulating film formed on a substrate to be processed.